1. Field of the Invention
The present invention relates to a method for manufacturing a display device having a stacked-layer structure including thin films. In particular, the present invention relates to a step of forming an opening in the thin films in a manufacturing process of the display device.
2. Description of the Related Art
A thin film transistor (hereinafter, also referred to as a “TFT”) and an electronic circuit using the thin film transistor are manufactured in such a manner that various thin films such as a semiconductor film, an insulating film, and a conductive film are stacked over a substrate and a predetermined pattern is appropriately formed by a photolithography technique. The photolithography technique is a technique in which a pattern of a circuit or the like which is formed of a material that does not transmit light over a transparent flat plate, which is referred to as a photomask, is transferred to an aimed substrate with the use of light. The photolithography technique has been widely used in a manufacturing process of a semiconductor integrated circuit or the like.
A conventional manufacturing process using the photolithography technique needs multiple steps such as exposure, development, baking, and peeling only for treating a mask pattern formed of a photosensitive organic resin material that is referred to as a photoresist. Therefore, manufacturing cost is inevitably increased as the number of the photolithography steps is increased. In order to solve such a problem, manufacture of a TFT, using reduced number of photolithography steps has been attempted (for example, see Patent Document 1: Japanese Published Patent Application No. 2000-133636). In Patent Document 1, a resist mask formed by a photolithography step is once used, and then the volume of the resist mask is expanded by swelling, so that the resist mask is used again as a resist mask with a different shape.